1. Field of the Invention
The present invention relates to a tray made of silica glass or ceramic material with seats made out of profiled elongated members provided with slots to serve as seats for disk-shaped elements such as round wafers.
2. Discussion of the Prior Art
A tray of this type is known from Gemeran Pat. No. 3 024 751, which discloses a tub-like seating component made out of lengths of silica-glass section with slots in the base and in the upward-oriented ends of the tub. The slots constitute a three-point support for the wafers inserted in them. The total weight of the wafer rests on the base of the tray when it is fresh from the factory and used for the first time, with the slots at the ends of the tub functioning only to position the wafers. Subject, however, to the weight of the wafers inserted in the tray and to the very high temperatures that the wafers are treated at and which the tray itself is also accordingly subjected to, the tray will deform slightly when used for a long period of time and the substrate itself will come into contact with the ends of the tub, resulting in a three-point support. A tray of this type must be practically constantly supported externally by special supporting frames. Trays of this type are limited both in that the material they are manufactured out of has to be thick enough to obtain the requisite strength and in the tolerances to which that they can be contoured and shaped.
Another tray, made out of rods and called a rod tray, is known from German Utility Model No. 8 021 868. It comprises four slotted silica-glass rods rigidly fused together by means of a silica-glass tube between the upper and lower rods. This type of rod tray has properties that are more desirable than those of any other type in that it consists of only a few parts, and of parts that are also uniform. Still, the freely suspended parts cannot be prevented from buckling once the tray has been used for a while.
The object of the present invention is to provide a tray made of silica glass or ceramic material for disk-shaped elements and especially for round wafers that is shaped in such a way as to provide easy access of process gas and loading/unloading tools, and is highly stable. The design principle allows easy adaptation to different wafer sizes.